Influenza A virus infection dynamics in two sow herds and effects of interventions.

To measure incidence and estimate temporal and spatial dynamics of porcine reproductive and respiratory syndrome virus (PRRSV) infection in US sow herds. 371 sow herds in the United States from 14 production companies. The exponentially weighted moving average was used to monitor incident PRRSV infections for onset of an epidemic. The spatial scan statistic was used to identify areas at significantly high risk of PRRS epidemics. A χ(2) test was used to estimate whether there were significant differences in the quarterly and annual PRRS incidence among time periods, and a bivariable logistic regression model was used to estimate whether PRRSV infection during a given year increased the odds of that herd being infected in the following year. During the 4-year period of this study, 29% (91/319; 2009 to 2010), 33% (106/325; 2010 to 2011), 38% (135/355; 2011 to 2012), and 32% (117/371; 2012 to 2013) of the herds reported new infections. Weekly incidence was low during spring and summer and high during fall and winter. The exponentially weighted moving average signaled the onset of a PRRSV epidemic during the middle 2 weeks of October each year. Disease incidence was spatially clustered. Infection in the previous year increased the odds of infection in 2010 to 2011 and 2011 to 2012. Results indicated a striking repeatability in annual PRRSV temporal and spatial patterns across 4 years of data among herds from 14 production companies, which suggested that efforts to control PRRSV at a regional level should continue to be supported.

Objective. Study the influence of Cladosporium cladosporioides metabolites on viral infection dynamics in potato plants under conditions of artificial and natural infection. Methods. Laboratory (virological, immunological, electron microscopic), field, statistical. Results. The influence of microbial metabolites on the development of viral infection in potato plants was studied in 2021 and 2022 under the conditions of a small field experiment. In 2021, under the conditions of protection against re-infection in the variants artificially infected with potato virus X (PVX), visual and immunological methods did not reveal any plants with symptoms of viral damage, the electron microscopic examination showed a low concentration of virus particles in plants, which probably caused due to abnormally high temperature during the vegetation of micro-plants. Treatment of plants with C. cladosporioides metabolites did not significantly affect the accumulation of PVX. In the experiments of 2022, tubers from healthy and artificially infected microplants from variants with and without treatment of plants with C. cladosporioides metabolites were used. The analysis of the viral infection dynamics under the conditions of natural infection with phytopathogenic viruses and previous artificial infection with PVX showed that C. cladosporioides metabolites affect the development of viral infection. In most variants using microbial metabolites, the rate of visual manifestation of the viral disease was 3 % to 5 % lower compared to the control. The frequency of detection of viruses by the immunological method was higher in the control variant and was equal to 40 %, the lowest number of detected infected plants was reported in the variant when the plants were treated with C. cladosporioides metabolites for two consecutive years and was equal to 22.5 %. The greatest decrease in the viral protein content, which indicates a decrease in virus reproduction, was reported when C. cladosporioides metabolites were applied in the first and second years in the variants artificially infected with PVX in 2021 — the difference to the control was 38 %. We believe that the influence of C. cladosporioides metabolites on the viral infection dynamics in potato plants is caused by exohormonal substances included in their composition. Conclusion. The results of two-year studies show that C. cladosporioides metabolites influence the viral infection dynamics. A decrease in the rate of visual manifestations of viral disease is registered. The lowest number of infected plants was found in the variant when the plants were treated with C. cladosporioides metabolites for consecutive two years. Also, the action of microbial metabolites reduces the concentra tion of viral protein in potato plants. Such a reaction of the “plant-virus” system indicates the inhibitory activity of C. cladosporioides metabolites against viruses.

Objective: To investigate the use of porcine reproductive and respiratory syndrome virus (PRRSV) reverse transcription-polymerase chain reaction (RT-PCR) on oropharyngeal scrapings concurrently with paired serological testing for detection of PRRSV infection in sows in commercial herds. Methods: Oropharyngeal scrapings were collected from 191 sows in a 1000-sow, commercial farrow-to-finish herd (Herd A) and from 56 sows in a 900-sow, commercial farrow-to-wean herd (Herd B). Sera were collected from all Herd A sows and 20 Herd B sows. An RT-PCR assay was used to amplify RNA extracted from oropharyngeal scrapings, and a commercial serum ELISA was used to assess PRRSV antibody levels. Results: Oropharyngeal scrapings from 28.3% of Herd A sows and 19.6% of Herd B sows were RT-PCR-positive for PRRSV. Administration of a killed swine influenza vaccine to 80% of Herd A sows 2 weeks before collection of oropharyngeal scrapings did not influence the rate of PRRSV detection. Sera from the 191 Herd A sows and 20 Herd B sows were negative for PRRSV by virus isolation. Virus isolation detected PRRSV in 36.4% of the RT-PCR-positive sows in Herd B. With RT-PCR results as an indicator of the true PRRSV status of the sow, paired ELISA testing had a sensitivity of 70.4% and a specificity of 49.6%. Implications: Oropharyngeal scrapings were RT-PCR-positive for PRRSV RNA in aviremic, clinically normal sows and in some sows with PRRSV ELISA sample: positive ratios <0.4. The diagnostic parameters of paired serological testing will likely preclude the use of this method for detecting PRRSV RT-PCR-positive sows.

Viral dynamics is the study of the population dynamics of viral infection within the body of an infected individual. It describes how viruses spread from cell to cell, with the aim of revealing the basic laws that govern the spread of the virus within the host, their interaction with the immune system, and their response to therapy. For viruses that produce a viremia, changes in the size of the virus population can be measured and followed from blood samples obtained by phlebotomy at various time intervals using very sensitive polymerase chain reaction (PCR)-based assays to quantify viral nucleic acids accurately over a dynamic range of six orders of magnitude. To analyze these data, mathematical models based on a firm understanding of the biology of the virus and its interaction with the host have been developed. Such models can often provide nonintuitive insights into the dynamics of viral infection. The advent of potent antiviral drugs for the treatment of viral diseases in recent years has facilitated the mathematical analysis of the dynamics of viral infections by providing a means for perturbing the steady state that commonly exists during chronic infection. Such studies have yielded not only insight into our understanding of the establishment, maintenance, and clearance of viral infection, but also predictors of response and principles useful in the design of more effective treatment strategies for human immunodeficiency virus (HIV) (1–4) and hepatitis C virus (HCV) (5,6) and promises to do the same for hepatitis B virus (HBV) as well. Importantly, viral dynamics analyses now offer a more sophisticated way of analyzing the response to therapy, particularly in Phase II clinical studies of short duration. Viral dynamics analysis maximizes the use of readily available data and allows different drugs, dosages and regimens to be compared more precisely. In this chapter, the basic model that has been formulated for HBV dynamics is explained and its application to the analysis of response to antiviral therapy is

The Dynamics of Virus and Rickettsial Infections. International Symposium Sponsored by the Henry Ford Hospital, Detroit, Michigan—October 21, 22 and 23, 1953 Geoffrey W. Rake CopyRight https://doi.org/10.2105/AJPH.44.10.1374-a Published Online: August 29, 2011

As the coronavirus disease (COVID-19) pandemic has evolved, the search for vaccines and treatments continues in earnest This pandemic is causing sharp increases in morbidity and mortality and an urgency to make therapies widely available The COVID-19 pandemic reveals the limited preparedness of health systems worldwide, and health care workers have very few options to combat this emergent disease and save patients' lives

Influenza A virus is being extensively studied because of its major impact on human and animal health. However, the dynamics of influenza virus infection and the cell types infected in vivo are poorly understood. These characteristics are challenging to determine, partly because there is no efficient replication-competent virus expressing an easily traceable reporter gene. Here, we report the generation of a recombinant influenza virus carrying a GFP reporter gene in the NS segment (NS1-GFP virus). Although attenuated when compared with wild-type virus, the NS1-GFP virus replicates efficiently in murine lungs and shows pathogenicity in mice. Using whole-organ imaging and flow cytometry, we have tracked the dynamics of influenza virus infection progression in mice. Imaging of murine lungs shows that infection starts in the respiratory tract in areas close to large conducting airways and later spreads to deeper sections of the lungs. In addition to epithelial cells, we found GFP-positive antigen-presenting cells, such as CD11b(+)CD11c(-), CD11b(-)CD11c(+), and CD11b(+)CD11c(+), as early as 24 h after intranasal infection. In addition, a significant proportion of NK and B cells were GFP positive, suggesting active infection of these cells. We next tested the effects of the influenza virus inhibitors oseltamivir and amantadine on the kinetics of in vivo infection progression. Treatment with oseltamivir dramatically reduced influenza infection in all cell types, whereas, surprisingly, amantadine treatment more efficiently blocked infection in B and NK cells. Our results demonstrate high levels of immune cells harboring influenza virus antigen during viral infection and cell-type-specific effects upon treatment with antiviral agents, opening additional avenues of research in the influenza virus field.

The objective of the study was to identify the features of seasonal and inter‐annual dynamics of avian influenza virus (AIV) infection in wild duck populations in the north of the Kulunda Plain during migrations. Biological samples were collected from April to November 2015–2024. from 15 species of wild ducks. To isolate influenza A virus isolates from cloacal smears, cultivation on developing chicken embryos was used in three consecutive passages, following a standard procedure. Cloacal smears were collected from 3,733 individuals of the Anatidae family. 163 A AIV VP isolates were isolated from samples taken in autumn, while 2 isolates were isolated in spring. The analysis of the data showed inter‐annual fluctuations in the infection rate of AIV from 1 to 10 % in different years. Varying seasonal and inter‐annual dynamics of wild duck infection were determined in the study area and it can be assumed that this is caused by the specific characteristics of the carriers and environmental conditions.

Human immunodeficiency virus type 1 (HIV-1) encodes four accessory genes: vif, vpu, vpr, and nef. Recent investigations using in vitro cell culture systems have shed light on the roles of these HIV-1 accessory proteins, Vif, Vpr, Vpu, and Nef, in counteracting, modulating, and evading various cellular factors that are responsible for anti-HIV-1 intrinsic immunity. However, since humans are the exclusive target for HIV-1 infection, conventional animal models are incapable of mimicking the dynamics of HIV-1 infection in vivo. Moreover, the effects of HIV-1 accessory proteins on viral infection in vivo remain unclear. To elucidate the roles of HIV-1 accessory proteins in the dynamics of viral infection in vivo, humanized mouse models, in which the mice are xenotransplanted with human hematopoietic stem cells, has been utilized. This review describes the current knowledge of the roles of HIV-1 accessory proteins in viral infection, replication, and pathogenicity in vivo, which are revealed by the studies using humanized mouse models.

In this paper, we propose a delayed viral infection model with mitosis of uninfected target cells, two infection modes (virus-to-cell transmission and cell-to-cell transmission), and immune response. The model involves intracellular delays during the processes of viral infection, viral production, and CTLs recruitment. We verify that the threshold dynamics are determined by the basic reproduction number $ R_0 $ for infection and the basic reproduction number $ R_{IM} $ for immune response. The model dynamics become very rich when $ R_{IM} > 1 $. In this case, we use the CTLs recruitment delay $ \tau_3 $ as the bifurcation parameter to obtain stability switches on the positive equilibrium and global Hopf bifurcation diagrams for the model system. This allows us to show that $ \tau_3 $ can lead to multiple stability switches, the coexistence of multiple stable periodic solutions, and even chaos. A brief simulation of two-parameter bifurcation analysis indicates that both the CTLs recruitment delay $ \tau_3 $ and the mitosis rate $ r $ have a strong impact on the viral dynamics, but they do behave differently.

BackgroundReproductive failure in sow herds due to infection with influenza A viruses has been described in the literature, but only a few studies have focused on the pathogenesis and the clinical signs of the infection. Case reports indicate an association between infections with influenza A viruses and reduced reproductive performance, although it has been difficult to experimentally reproduce the clinical outcome of poor reproductive performance. The aim of the present longitudinal field study was to compare the reproductive performance parameters before and after the implementation of vaccination against the influenza A (H1N1)pdm09 virus in sow herds infected with pandemic influenza A virus. Therefore, farm-specific data of 137 sow herds in Germany, including 60,153 sows, as well as the clinical presentation of the infection were surveyed via questionnaire. Furthermore, average performance parameters (return to oestrus rate, abortion rate, stillbirth rate, number of piglets born alive per litter, preweaning mortality rate and number of piglets weaned per sow per year) were recorded for 6 months before vaccination and 6 months after completion of primary vaccination.ResultsIn 79.8% of the farms, the clinical presentation of the infection was characterised by a reduced reproductive performance. These findings were confirmed by analysis of the performance parameters, which revealed a significant decline in the return to oestrus rate (p < 0.001), abortion rate (p < 0.001) and preweaning mortality rate (p = 0.023) and a significant increase of the number in piglets born alive (p = 0.001) and piglets weaned per sow per year (p < 0.001) after immunisation. The stillbirth rate did not change significantly.ConclusionThe present study represents the first attempt to demonstrate the association of influenza A virus infection, vaccination and the alteration in reproductive performance parameters, investigating a large number of cases. The results show that by vaccinating against the influenza A (H1N1)pdm09 virus, an improvement in reproductive performance can be achieved in sow herds infected with pandemic influenza A virus. Additionally, the large number of herds that were affected by poor reproductive performance after infection with the aforementioned virus confirms the assumption of an association between pandemic influenza A virus and reproductive losses.

The role of spatial factors in the success of an Aujeszky's disease eradication programme in a high pig density area (Northeast Spain, 2003–2007)

H9N2 avian influenza viruses (AIVs) continuously cross the species barrier to infect mammalians and are repeatedly transmitted to humans, posing a significant threat to public health. Importantly, some H9N2 AIVs were found to cause lethal infection in mice, but little is known about the viral infection dynamics in vivo. To analyze the real-time infection dynamics, we described the generation of a mouse-lethal recombinant H9N2 AIV, an influenza reporter virus (VK627-NanoLuc virus) carrying a NanoLuc gene in the non-structural (NS) segment, which was available for in vivo imaging. Although attenuated for replication in MDCK cells, VK627-NanoLuc virus showed similar pathogenicity and replicative capacity in mice to its parental virus. Bioluminescent imaging of the VK627-NanoLuc virus permitted successive observations of viral infection and replication in infected mice, even following the viral clearance of a sublethal infection. Moreover, VK627-NanoLuc virus was severely restricted by the K627E mutation in PB2, as infected mice showed little weight loss and a low level of bioluminescence. In summary, we have preliminarily established a visualized tool that enables real-time observation of the infection and replication dynamics of H9N2 AIV in mice, which contributes to further understanding the mechanisms underlying the pathogenic enhancement of H9N2 AIV to mice.

Summary This paper reviews our studies on the dynamics of pseudorabies virus (PRV) infections in populations of vaccinated pigs. By using mathematical models, experiments, and field observations, we have been able to quantify PRV transmission by the reproduction ratio R, which is defined as the average number of secondary cases caused by one infectious individual. If R is less than 1, PRV infections will fade out in the pig population and eradication is certain. Under experimental conditions, R of double‐vaccinated pigs was estimated at 0.3. In the field, R was estimated at 0.7 among multiple‐vaccinated breeding pigs, 3.4 among single vaccinated finishing pigs, and 1.5 among double‐vaccinated finishing pigs. So far, no risk factors have been identified that explain the difference between the transmission among double‐vaccinated pigs in the field and under experimental conditions. The implications of the transmission characteristics of the different types of pigs for the Dutch PRV eradication campaign are discussed. The structure of the PRV research programme described in this paper, in which knowledge of the interaction of the virus with individual pigs is extrapolated to the interaction of the virus with pig populations, can serve as an example for other research programmes that study infectious diseases.

Dynamics of viral infections: incorporating both the intracellular and extracellular levels